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Most planets orbit a star, but some planets can escape and “go rogue.” But how do astronomers study planets that wander the cold dark of interstellar space?

Join our host, Summer Ash of the National Radio Astronomy Observatory, as she talks about how radio astronomers study rogue planets.

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Evidence shows violent collapse responsible for formation of Jupiter-like protoplanet

A lucky cosmic alignment has revealed a single source of light in the first billion years after the big bang, setting up a major confirmation for the James Webb Space Telescope in its rookie year.

The NHFP exemplifies NASA's pursuit of excellence in astrophysics through support of some of the world's most promising and innovative young astrophysicists.

Scientists studying V Hydrae (V Hya) have witnessed the star’s mysterious death throes in unprecedented detail. Using the Atacama Large Millimeter/submillimeter Array (ALMA) and data from the Hubble Space Telescope (HST), the team discovered six slowly-expanding rings and two hourglass-shaped structures caused by the high-speed ejection of matter out into space. The results of the study are published in The Astrophysical Journal.

V Hya is a carbon-rich asymptotic giant branch (AGB) starStarA giant ball of hot gas that creates and emits its own radiation through nuclear fusion. located approximately 1,300 light-years from Earth in the constellation Hydra. More than 90-percent of stars with a mass equal to or greater than the Sun evolve into AGB stars as the fuel required to power nuclear processes is stripped away. Among these millions of stars, V Hya has been of particular interest to scientists due to its so-far unique behaviors and features, including extreme-scale plasma eruptions that happen roughly every 8.5 years and the presence of a nearly invisible companion star that contributes to V Hya’s explosive behavior.

“Our study dramatically confirms that the traditional model of how AGB stars die—through the mass ejection of fuel via a slow, relatively steady, spherical wind over 100,000 years or more—is at best, incomplete, or at worst, incorrect,” said Raghvendra Sahai, an astronomer at NASA’s Jet Propulsion Laboratory, and the principal researcher on the study. “It is very likely that a close stellar or substellar companion plays a significant role in their deaths, and understanding the physics of binary interactions is both important across astrophysics and one of its greatest challenges. In the case of V Hya, the combination of a nearby and a hypothetical distant companion star is responsible, at least to some degree, for the presence of its six rings, and the high-speed outflows that are causing the star’s miraculous death.” 

Mark Morris, an astronomer at UCLA and a co-author on the research added, “V Hydra has been caught in the process of shedding its atmosphere—ultimately most of its mass—which is something that most late-stage red giant stars do. Much to our surprise, we have found that the matter, in this case, is being expelled as a series of outflowing rings. This is the first and only time that anybody has seen that the gas being ejected from an AGB star can be flowing out in the form of a series of expanding ‘smoke rings.’”

The six rings have expanded outward from V Hya over the course of roughly 2,100 years, adding matter to and driving the growth of a high-density flared and warped disk-like structure around the star. The team has dubbed this structure the DUDE, or Disk Undergoing Dynamical Expansion. 

“The end state of stellar evolution—when stars undergo the transition from being red giants to ending up as white dwarf stellar remnants—is a complex process that is not well understood,” said Morris. “The discovery that this process can involve the ejections of rings of gas, simultaneous with the production of high-speed, intermittent jets of material, brings a new and fascinating wrinkle to our exploration of how stars die.”

Sahai added, “V Hya is in the brief but critical transition phase that does not last very long, and it is difficult to find stars in this phase, or rather ‘catch them in the act. We got lucky and were able to image all of the different mass-loss phenomena in V Hya to better understand how dying stars lose mass at the end of their lives.”

In addition to a full set of expanding rings and a warped disk, V Hya’s final act features two hourglass-shaped structures—and an additional jet-like structure—that are expanding at high speeds of more than half a million miles per hour (240 km/s). Large hourglass structures have been observed previously in planetary nebulae, including MyCn 18 —also known as the Engraved Hourglass Nebula—a young emission nebula located roughly 8,000 light-years from Earth in the southern constellation of Musca, and the more well-known Southern Crab Nebula, an emission nebula located roughly 7,000 light-years from Earth in the southern constellation Centaurus. 

Sahai said, “We first observed the presence of very fast outflows in 1981. Then, in 2022, we found a jet-like flow consisting of compact plasma blobs ejected at high speeds from V Hya. And now, our  discovery of wide-angle outflows in V Hya connects the dots, revealing how all these structures can be created during the evolutionary phase that this extra-luminous red giant star is now in.” 

Due to both the distance and the density of the dust surrounding the star, studying V Hya required a unique instrument with the power to clearly see matter that is both very far away and also difficult or impossible to detect with most optical telescopes. The team enlisted ALMA’s Band 6 (1.23mm) and Band 7 (.85mm) receivers, which revealed the star’s multiple rings and outflows in stark clarity. 

“The processes taking place at the end stages of low mass stars, and during the AGB phase in particular, have long fascinated astronomers and have been challenging to understand,” said Joe Pesce, an astronomer and NSF program officer for NRAO/ALMA. “The capabilities and resolution of ALMA are finally allowing us to witness these events with the extraordinary detail necessary to provide some answers and enhance our understanding of an event that happens to most of the stars in the Universe.”

Sahai added that the incorporation of infrared, optical, and ultraviolet data into the study created a complete multi-wavelength picture of what might be one of the greatest shows in the Milky Way, at least for astronomers. “Each time we observe V Hya with new observational capabilities, it becomes more and more like a circus, characterized by an even bigger variety of impressive feats. V Hydrae has impressed us with its multiple rings and acts, and because our own Sun may one day experience a similar fate, it has us at rapt attention.” 

Research

• “The rapidly evolving AGB star, V Hya: ALMA finds a multi-ring circus with high velocity outflow,” Sahai et al, (2022), The Astrophysical Journal, preprint: arXiv:2202.09335

Resources

• “Discovery of very high velocity outflow in V Hydra – Wind from an accretion disk in a binary?” Sahai, R. & Wannier, P. G. (1988), Astronomy & Astrophysics, ADS: 1988A&A…201L…9S
• “V Hydrae: the missing link between spherical red giants and bipolar planetary nebulae? Radio observations of the molecular envelope,” Kahane et al (1996), Astronomy & Astrophysics, ADS: 1996A&A…314..871K
• “A collimated, high-speed outflow from the dying star V Hydrae,” Sahai et al (2003), Nature, 426, 261, doi.org/10.1038/nature02086
• “High-velocity bipolar outflow and disklike envelope in the carbon star V Hydrae,” Hirano et al (2004), The Astrophysical Journal, doi: 10.1086/424382
• “High-Speed Bullet Ejections during the AGB to Planetary Nebula Transition: HST Observations of the Carbon Star, V Hydrae,” Sahai, R., Scibelli, S., & Morris, M.R. (2016), The Astrophysical Journal, doi.org/10.3847/0004-637x/827/2/92

About ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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Astronomers have discovered more than 5,000 planets orbiting other stars. We now know that most stars have orbiting planets and we have a good idea of how they form. Within star-forming regions, most young stars have a disk of gas and dust around them known as a protoplanetary diskProtoplanetary DiskThe swirling disk of dust and gas that collapsed from a much larger cloud of material that will eventually evolve into a fully fledged planetary system. Features in the disk may already herald the presence of young planets.. Astronomers have observed early planets forming within these disks. But astronomers are still not sure how protoplanetary disks form and evolve

Studying the earliest period of planetary formation is difficult. Young stars are surrounded by a dense halo of dust that can hide them from view, and by the time the dust clears a protoplanetary disk has already formed. To understand this process better, astronomers using the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) have undertaken a radio survey of young stars in the constellation of Orion, which is home to the closest star-forming regions to Earth. This new survey is known as the VLA/ALMA Nascent Disk and Multiplicity (VANDAM) survey, and it is the largest survey of young stars ever made.

Although the dust surrounding young stars blocks most visible light, it is more transparent to radio light. Because of this, the radio Credit:  observations of the VLA and ALMA allowed astronomers to have a detailed view of young star systems. With the VANDAM survey, the team measured the size and mass of many young protoplanetary disks and compared them to older disks ALMA has already studied. One of the things they found was that younger disks are generally more massive than older disks of the same size. This makes sense since as a star forms it captures more nearby material, which reduces the mass of its surrounding disk. But it also implies that the largest worlds of a planetary system start to form early on when the protoplanetary disk is more dense.

Older protoplanetary disks typically have rings within them where there is significantly less material. These gaps within the disk are often regions where planets are forming, but they could also indicate a resonant structure within the disk, where the gravitational tug of young planets causes gaps to form, similar to the way Jupiter creates orbital gaps in the asteroid belt. VANDAM observations have found similar gap structures within disks as young as 100,000 years, which is surprisingly early. Within the first million years of a system, the structure of a disk is similar to that of older disks. A few of the systems seen in the VANDAM survey were very irregular in shape. It’s possible that these systems are so young that a disk system hasn’t begun to form. It could also be the case that even the protostar hasn’t fully taken shape.

Working together, the VLA and ALMA are giving us a better understanding of the complex dance of gravity and matter around young stars, and how that dance leads to the formation of planets like our own.

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The National Radio Astronomy Observatory (NRAO) Jansky Fellowship program provides outstanding opportunities for research in astronomy. Jansky Fellows formulate and carry out investigations either independently or in collaboration with others within the wide framework of interests of the observatory. The program is open each fall to candidates with interest in radio astronomy techniques, instrumentation, computation, and theory. Multi-wavelength projects leading to a synergy with NRAO instruments are encouraged. We are pleased to announce that four new Jansky Fellows will join NRAO in the fall of 2022.

Rebecca Charbonneau earned her Ph.D in History and Philosophy of Science from the University of Cambridge in 2021. Her dissertation focused on the history of radio astronomy and examined the challenges and benefits of international scientific collaboration during the Cold War period. She subsequently worked as the historian-in-residence at the Center for Astrophysics | Harvard & Smithsonian (CfA), during which time she led a project on preserving indigenous astronomical heritage. As a Jansky Fellow, her research program will make use of NRAO’s historical archives and will focus on the history of international cooperation within radio astronomy.

Tao-Chung Ching performed his Ph.D study at the National Tsing-Hua University, Taiwan, and CfA under the supervision of Shih-Ping Lai and Qizhou Zhang. He later became a FAST (Five-hundred-meter Aperture Spherical radio Telescope) fellow at the National Astronomical Observatory of China working with Di Li. His research interests are interstellar magnetic fields and star formation studied through observational astronomy from submillimeter to radio wavelengths. Using FAST, Tao-Chung has obtained the first Zeeman-effect detection of the HI Narrow Self-Absorption (HINSA) future. As a Jansky Fellow at NRAO in Socorro, he will use the VLA to explore HINSA as a systematic Zeeman probe, measuring magnetic field strengths of star-forming regions at high angular resolutions.

Dillon Dong completed his Ph.D in 2022 at Caltech with Gregg Hallinan. Dillon is broadly interested in astronomical objects that evolve over human timescales, and how they interact with their local and large-scale surroundings. He uses a combination of multi-wavelength observations and order-of-magnitude theory to characterize variable and transient sources that he identified in the VLA Sky Survey (VLASS). His current projects involve using supernovae as probes of pre-explosion eruptive mass loss, statistical characterization of black hole and stellar flares, and identifying radio transients with unusual spectral properties. As a Jansky Fellow at NRAO in Socorro, he will continue his study of VLASS transients and variables, with a focus on luminous, extragalactic radio transients. He also will continue his development of flexible tools to automate the detection of transients and variables in future VLA observations.

Michael Rugel investigates the multiphase interstellar medium (ISM) with surveys of the Milky Way at radio wavelengths. His research focuses on the formation of molecular clouds, as well on feedback on them with studies of tracers of atomic, molecular and ionized gas. As a Jansky Fellow at the Center for Astrophysics | Harvard & Smithsonian and at NRAO Socorro, Rugel will expand his research on star formation, and structure and evolution of the ISM with the THOR-GC survey, an extension of The HI, OH, Recombination Line survey of the Milky Way (THOR) to the Galactic center, and the Bar and Spiral Structure Legacy survey (BeSSeL) extension to the southern Milky Way.

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